Thousands of demonstrators marched Sunday in European cities in a show of anti-austerity solidarity on the eve of an emergency summit aimed at keeping the debt-ridden Greek government from defaulting on its European loan payments.

The rallies in Athens, Brussels and Amsterdam came as Greek Prime Minister Alexis Tsipras held separate phone talks with the leaders of France, Germany and the European Commission, in search of an elusive cash-for-reforms deal by a June 30 deadline.

Without a deal, Greece is expected to default on a $1.8 billion loan repayment to the International Monetary Fund, setting the stage for its possible departure from the 19-nation eurozone.

A statement Sunday from the Athens government press office said Tsipras offered a "proposal for a mutually beneficial agreement" providing a "permanent solution" to the standoff. It did not provide details.

Monday's summit was called after multi-national talks about terms of the ongoing $17.5 billion Greek bailout collapsed last week over Athens' refusal to adopt new austerity measures demanded by its European creditors.

Demonstrators said the financial sector should take responsibility for the damage it caused.

Britain's Guardian newspaper, quoting officials close to the negotiations, said creditors are proposing a plan to extend the bailout by six months and provide nearly $15 billion in emergency relief.

The report said negotiations continued late into Sunday evening and that a breakthrough hinged on Greece agreeing to further austerity measures that it has so far resisted.

In a stop-gap move Friday, the European Central Bank (ECB) agreed to extend an additional $3.4 billion to Greek banks, after worried customers withdrew more than $4 billion in savings in the past week.

Reuters news agency reported Sunday that an additional $1.1 billion was withdrawn since then, and said the ECB was considering further financial help over fears that Greek banks would be unable to open Tuesday.